On 23/06/2017 20:05, NY wrote:
"Tim Watts" wrote in message
...
On 23/06/17 19:21, ss wrote:
Not being electrically savvy but should the `trip` switch on the
mains meter not have clicked in and cut the current off to prevent a
fir starting.

What trip switch?

The over-current or earth leakage trip-switches in the "fuse box". Or in
extreme case the 60 A "company fuse" (which i think is always still an
old-fashioned melting-metal fuse). But I think you *did* know that.

ELCB may potentially save you if the cable chars or melts sufficiently
to allow a live to earth current that trips it out. But if you are out
of luck the leak goes live to neutral and a nominal 13A fuse will
support something like 20A for a few minutes...

Seen that happen with internally molten overloaded extension leads that
haven't been unwound properly. All the ones in out village hall now have
thermal cutouts to defend against potential abuse.

The difficulty is when the short is not to earth and is a
lower-than-normal resistance but not a complete short, so you draw a
larger current (or a current through the wrong material, allowing it to
heat up) but not a current that is large enough to blow/trip the cutout.

It is particularly bad in those tall floor fan heaters that swivel from
side to side with a 13A fuse and a cable that is forever being twisted
to and fro when the thing is in use and allowed to move as designed.

It isn't really a case of if it fails so much as when...

--
Regards,
Martin Brown